Re: pigs and other novice questions

At 07:31 PM 10/05/1999 -0400, you wrote:
>Ok, so I'm a newbie.  By reading your chatter for a few days I have surmised 
>the following:
>1. Some of you guys are using pole pigs in reverse as an input xfmr for your 
>TC (see, I have the language down already).
>2. You are running them on 240 vac but using current limiting devices in 
>series (I assume to keep from sucking the guts out of your fuse box).
>3. You are looking to achieve an input current of around 10 to 50 amps, which 
>I'm guessing is less than 10% of what you'd see if it were direct connected 
>to 240 vac.

Absolutely correct!

>So here's my question: Why don't you input 120 vac instead of 240, and have 
>less voltage to drop?  Or better yet, use that welder's secondary to drive 
>the pig, since the welder puts out current-limited voltages in the range of 
>20-50 vac?  Or use big fat SCR's to chop the input waveform?  (Or do you need 
>nice clean sine waves?)  Am I missing something?

when one inputs 240 volts you get 14400 volts on the output.  If you input
only 120 volts you would get 7200 volts.  Since the energy in the primary
cap is proportional to the voltage squared (assuming some things...), you
would only get 1/4 power to the coil.  However, with a choke in line with
the pig.  You can get the full 14400 volts to charge the primary cap but
still have current limiting to keep from blowing up the input AC.  A short
on the pigs output (like every time the gap fires) could draw 2000 amps
from the AC line.  However, the series inductance (or resistance too) stops
that current surge and limits it to a very nice level if done right.

>I'll be good and only ask this one question.  Maybe next time I can get some 
>of you to help me troubleshoot my first TC (15kv 30 ma NST, 8 turn 9" pri, 
>12" 800 turn sec, 4.5"x1.25" toroid).

My first guess would be that you need more turns on the primary.  Your
secondary is probably tuned to around 330kHz but the primary is probably in
the 400kHz range if you are using a 10nF cap or 560kHz with a 5nF cap.
Really need to know the inner diameter of the primary and the pitch or
outer diameter to be sure.  Also, the primary cap value too...  It sure
sounds like the primary needs a lower frequency to match the secondary.